Developer composition for positive photoresists using solution with cyclic quaternary ammonium hydroxides

ABSTRACT

A method of developing a positive photoresist layer which has been image-wise-exposed comprising contacting the layer with an alkaline developing composition to remove exposed areas of the layer, the developing composition comprising a solution containing a cyclic quaternary ammonium hydroxide developing agent in a sufficient concentration to remove exposed areas of the layer. The present invention also includes a developing composition for use in the method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to developers for positive photoresists.

2. Description of the prior art

Various compounds are disclosed in the prior art as being suitable foruse as developers for positive photoresists. Exposure of a positivephotoresist to actinic radiation results in a solubility differentialbetween the exposed and unexposed areas such that treatment with anappropriate developer results in removal of the radiation-struck areasand retention of the desired image areas on the support. The criteriafor a suitable photoresist developer are speed of development, highselectivity between exposed and unexposed areas, high basicity, andsolubility of exposed resin for removal from the film surface.

A typical listing of suitable bases for use as developers appears inU.S. Pat. No. 3,887,450. Included are various primary, secondary,tertiary amines and hydroxyamines; cyclic amines; polyamines; watersoluble basic salts of the above; and ammonium hydroxide andtetrasubstituted ammonium hydroxides. In spite of these extensive lists,the most commonly used developers for positive acting photoresists arealkylammonium hydroxides, such as tetramethyl ammonium hydroxide.

U.S. Pat. No. 4,294,911 describes a developing composition comprising aquaternary alkanol ammonium hydroxide developing agent and a stabilizingconcentration of a sulfite. The developing composition is stated to beuseful for developing light-sensitive compositions containing a quinonediazide. In the preferred embodiment, the quaternary alkanol ammoniumhydroxide is methyl triethanol ammonium hydroxide. Such compounds areknown in the prior art, but have suffered from the disadvantage oflimited shelf-life. Thus, the '911 patent discloses the use of sulfiteas a stabilizer.

However, such compositions continue to suffer from severaldisadvantages. Although the structure provides certain surfactant-likeproperties, the concomitant foaming would be a disadvantage duringprocessing. Moreover, the relatively higher molecular weight than thesimple quaternary ammonium compounds of the prior art, e.g., tetramethylammonium hydroxide, tends to increase the development time.

Because of these and other disadvantages, commercially, the simplecuaternary ammonium compounds have continued to be the preferreddeveloping agents. These simple quaternary ammonium developers however,do not exhibit the degree of differential solubilization for exposed andunexposed photoresist that is required to achieve the fine linedefinition required for advanced microcircuits.

Accordingly, a need exists for compounds which exhibit greaterdifferential solubilization properties towards resins currently used inpreparing positive-acting photoresists, and which are more stronglybasic and thus better developing agents than the compounds currentlyused.

SUMMARY OF THE INVENTION

The present invention is a method of developing a positive photoresistlayer which has been image-wise-exposed. The method comprises contactingthe layer with an alkaline developing composition to remove exposedareas of the layer, the developing composition comprising a solutioncontaining a cyclic quaternary ammonium hydroxide developing agent in asufficient concentration to remove exposed areas of the layer.

The present invention also includes a positive photoresist compositionwhich comprises a solution of a cyclic quaternary ammonium hydroxidedeveloping agent, the solution having a normality between about 0.1 Nand about 6.0 N.

DETAILED DESCRIPTION OF THE INVENTION

The method of the present invention uses a developing agent which is acyclic quaternary ammonium hydroxide. By "cyclic quaternary ammoniumhydroxide" is meant a compound in which a quaternarv substitutednitrogen is a member of an aromatic or nonaromatic ring of between 4 and8 atoms, the counterion being hydroxide ion. The quaternary nitrogencontaining ring optionally includes additional heteroatoms such assulfur, oxygen, or nitrogen. The quaternary nitrogen containing ring mayalso be one ring of a bicyclic or tricyclic compound. The quaternarynitrogen atom is substituted by one or two groups depending on whetherthe ring is aromatic or nonaromatic. Where two groups are present, theymay be the same or different. The quaternary nitrogen substitution ispreferably an alkyl group or groups of one to four carbon atoms, andmore preferably methyl. The remaining members of the quaternary nitrogenring may also be substituted, if desired.

It is preferred that the quaternary nitrogen be a member of an aromaticring, and more preferably a pyridinium ring. A preferred pyridiniumcompound is N-methyl pyridinium hydroxide, particularly when thepositive photoresist layer has been prepared from a novalac resin.

While not wishing to be bound by theory, it is believed that thedeveloping composition of the present invention obtains its superiordeveloping properties from the similarity between the structure of themonomer units used in preparing the photoresist, and the structure ofdeveloping agent. Thus, photoresists made from novalac resins, i.e.,resins which include a phenyl ring, are readily developed by thepreferred developing agent, N-methyl pyridinium hydroxide. Thesimilarity of structure is believed to contribute to the solubility ofthe resin in the developing composition. Moreover, it is believed thatthe planar structure of the cyclic compounds and that either two orthree of the bonds of the quaternary nitrogen are sterically restrictedby the ring structure and held back from the hydroxide ion, contributeto produce compounds having considerably less steric hindrance to attackon the exposed resin than the quaternary ammonium compounds of the priorart.

It is preferred that the cyclic quaternary ammonium hydroxide used inthe method of the present invention be matched as nearly as possible tothe resin of the photoresist in the sense discussed above, i.e., using apyridine derivative when a novalac resin is being employed. Accordingly,derivatives of the nitrogen heterocyclic compounds in Table I may beused in the practice of the present invention.

                  TABLE I                                                         ______________________________________                                        Pyridine            Purine                                                    Pyrrole             Carbazole                                                 Isopyrroles         Diazepine                                                 Pyrazole            Azepine                                                   Triazole            Indole                                                    Oxazole             Indolemine                                                Isoxazole           Isobenzazole                                              Thiazole            Pyrindine                                                 Isothiazoles        Pyranol-pyrrole                                           Oxadiazoles         Isoindazole                                               Dioxazole           Indoxazine                                                Pyridazine          Benzoxazole                                               Pyrimidine          Anthranil                                                 Pyrazine            Quinoline                                                 Piperazine          Isoquinoline                                              Triazine            Cinnoline                                                 Oxazine             Quinazoline                                               Isoxazine           Naphthridine                                              Oxathiazine         Pyrido-pyridine                                           Oxadiazine          Benzoxazine                                               Morpholine          Benzisoxazine                                             Acridine            Imidazoline                                               Oxatriazoles        Pyrrolidone                                               ______________________________________                                    

The compounds in Table I are readily quaternized by methods well knownin the art. For example, the N-methyl derivative may be made by reactionwith methyl chloride, followed by ion exchange to convert the chlorideto the hydroxide. Examples of compounds which can be produced in thismanner include:

N,N-dimethyl-N'-methyl pyrazinium hydroxide

N,N-dimethyl morpholinium hydroxide

N-methyl-N'-methyl imidazolinium hydroxide

N,N-dimethyl imidazolinium hydroxide

Aqueous solutions of the developing agents are preferred in the practiceof the method of the present invention. However, both protic andnon-protic polar organic solvents may also be used including alcohols,ketones, and solvents such as dimethylofomamide.

The developers of the present invention may be advantageously employedto develop novolac-type positive photoresists. Such photoresists arewell known to those skilled in the art, and are typified by aphotoresist sold by Dynachem Corporation (a subsidiary of Morton ThiokolInc.) under the trademark OFPR-800, or that sold by Philip A. HuntChemical Co. under the trademark HUNT WAYCOAT 204.

In the developing compositions of this invention, the cyclic quaternaryammonium hydroxide compound can be employed in any concentrationsufficient to act as a developing agent. Preferably, the developingcomposition employed as a working solution is an aqueous solution of thecyclic quaternary ammonium hydroxide having a normality between about0.1 N and about 6.0 N, and more preferably between about 0.2 N and about0.5 N. The optimum concentration of cyclic quaternary ammonium hydroxideis dependent upon a number of factors, such as the particular compoundutilized, the particular light-sensitive material to which thedeveloping composition is applied, and the desired development time.Typically, the developing compositions are prepared in the form ofaqueous concentrates, having a much higher concentration of cyclicquaternary ammonium hydroxide than is desired in the working solutionand then are diluted with water.

The present invention also includes a positive photoresist developingcomposition which is described above for use in the method of thepresent invention. The developing composition comprises a solution of acyclic quaternary ammonium hydroxide developing agent, the solutionhaving a normality between about 0.1 N and about 6.0 N.

Photoresist developers employed in the semiconductor industry must beessentially free of metal ion contaminants, such as sodium or potassiumions, which can deteriorate the substrate conductivity and adverselyaffect important properties of the integrated circuit device such aselectrical resistivity. Thus, in a preferred embodiment of the presentinvention, the developing composition is free, or at least substantiallyfree, of metal ions.

The compositions for use in the present invention can also contain asurfactant. Suitable surfactants for such use are well known to thoseskilled in the art.

In order to further illustrate the present invention and the advantagesthereof, the following specific examples are given, it being understoodthat these examples are intended only to be illustrative without servingas a limitation on the scope of the present invention.

EXAMPLE 1

Example 1 illustrates the synthesis of N-methyl pyridinium hydroxide, adeveloping agent for use in the present invention.

Into a 500 ml three neck round bottom flask fitted with heating mantel,magnetic stirrer, thermometer, gas dispersion tube, and condenser, isadded 200 ml of pyridine (99+% ultrapure, Alfa Products). The pyridineis heated to 32° C. and then methyl chloride (CH₃ Cl) is slowly bubbledin. Within 30 minutes (T=41° C.) the solution becomes cloudy. Methylchloride addition is continued with stirring for 4 hours and thetemperature maintained at 50° C. Total CH₃ Cl addition is 51.5 g. Aftercooling, the solution is filtered and the white crystalline N-methylpyridinium chloride is recovered and vacuum dried at 60° C. overnight.The yield is 26.65 g. After standing for several days, more productprecipitates out of the filtrate. The mixture is filtered again and thewhite crystalline product vacuum dried at 60° C. overnight. Theadditional yield is 10.72 g.

N-methyl pyridinium chloride (17.8 g) is dissolved in 28.2 g ofdeionized distilled water, diluted to 65 ml, and passed through an ionexchange column containing 340 g of resin sold by Rohm & Haas Co. underthe trademark NUCLEAR GRADE AMBERLITE IRN-78, HYDROXIDE FORM. Theresultihg aqueous solution of N-methyl pyridinium hydroxide issubsequently diluted with deionized distilled water to a concentrationof 3.85 wt. % (0.35 N).

EXAMPLE 2 AND COMPARATIVE EXAMPLES A-G

To test the developing agent prepared in Example 1, a variety of similarcompounds and developing agents of the prior art are compared withN-methyl pyridinium hydroxide. The compounds are as follows:

    ______________________________________                                        Example(s)  Developing Agent                                                  ______________________________________                                        2           N--methyl pyridinium hydroxide                                    A, E        methyl trihydroxyethylammonium                                                hydroxide                                                         B, F        beta-hydroxyethyltrimethylammonium                                            hydroxide                                                         C, G        tetrahydroxyethylammonium hydroxide                               D           tetramethylammonium hydroxide                                     ______________________________________                                    

Each of the developing agents is added to deionized water to prepare anapproximately 0.36 N solution, this normality being chosen forcomparison against the developing agent of Example D which iscommercially available from Philip A. Hunt Chemical Co. under thetrademark HUNT-WAYCOAT WX-108-4, itself a 0.36 N solution.

The normality of the resulting solutions and the basicity (pK_(b)) areas follows:

    ______________________________________                                                     Concentration                                                    Example(s) wt. %        N       pK.sub.b                                      ______________________________________                                        2          3.85         0.35    1.29                                          A, E       6.18         0.34    2.83                                          B, F       4.13          0.349  1.91                                          C, G       7.58          0.359  1.54                                          D          3.27         0.36    2.38                                          ______________________________________                                    

Example 2, the N-methyl pyridinium hydroxide composition of the presentinvention, desirably exhibits the lowest pK_(b) value, i.e., the highestbasicity of the five developers listed.

The developing compositions are tested on resist coatings prepared byapplying two spray coats of hexamethyldisilane to a silicon wafer,followed by application of a resist layer using HUNT WAYCOAT 204Photoresist and standard wafer-coating equipment. The resist layer issubsequently prebaked at standard temperature and imagewise exposed witha Perkin Elmer Scanning UV machine having a UV source of about 1000watts.

Developing is performed by placing the exposed resist coated slice in acontainer of developing composition and agitating for 20 seconds, exceptfor Examples E, F and G which are left in developing composition for 5minutes. The developed slices are then removed from the developingcomposition and rinsed in a beaker of deionized water for 2 seconds tostop development, followed by a 15 second rinse under deionized water tocompletely clean the slice of developer.

Microscopic examination of the developed wafers revealed superior linedefinition and selectivity for exposed versus unexposed photoresist whenemploying the composition of Example 2, relative to the compositions ofExamples A, B and C.

The developing composition of Example 2 is comparable to thecommercially available developing composition of Comparative Example D.Comparative Examples A, B, and C do not provide acceptable developmenteven when the development time is extended to 5 minutes in ComparativeExamples E, F and G.

Although the above discussion has been directed primarily to a methodusing the compositions as photoresist developers, the compositions canalso be used in other applications, such as RTV (Room TemperatureVulcanizing) Strippers and etchants.

While the invention has been described in terms of various preferredembodiments, one skilled in the art will appreciate that variousmodifications, substitutions, omissions, and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims.

What is claimed is:
 1. A positive photoresist developing compositionconsisting essentially of a solution of a cyclic quaternary ammoniumhydroxide developing agent in which a quaternary substituted nitrogen isa member of an aromatic or nonaromatic ring of between 4 and 8 atoms;said developing agent being present in a concentration sufficient to actas a developing agent, the solution having a normality of the cyclicquaternary ammonium hydroxide between about 0.1 N and about 6.0 N. 2.The composition of claim 1 wherein the cyclic quaternary ammoniumhydroxide is a derivative of pyridine, purine, pyrrole, carbazole, anisopyrrole, diazepine, pyrazole, azepine, triazole, indole, oxazole,indolemine, isoxazole, isobenzazole, thiazole, pyrindine, anisothiazole, pyranolpyrrole, an oxadiazole, isoindazole, dioxazole,indoxazine, pyridazine, benzoxazole, pyrimidine, anthranil, pyrazine,quinoline, piperazine, isoquinoline, triazine, cinnoline, oxazine,quinazoline, isoxazine, naphthridine, oxathiazine, pyrido-pyridine,oxadiazine, benzoxazine, morpholine, benzisoxazine, acridine,imidazoline, an oxatriazole, or pyrrolidone.
 3. The composition of claim1 wherein the quaternary nitrogen of the cyclic quaternary ammoniumhydroxide is within an aromatic ring.
 4. The composition of claim 3wherein the cyclic quaternary ammonium hydroxide is an N-alkylsubstituted pyridinium hydroxide.
 5. The composition of claim 4 whereinthe alkyl group on the quaternary nitrogen is of one to four carbonatoms.
 6. The composition of claim 4 wherein the cyclic quaternaryammonium hydroxide is N-methyl pyridinium hydroxide.
 7. The compositionof claim 1 wherein the normality of the developing agent within thedeveloping composition is between about 0.2 N and about 0.5 N.
 8. Thecomposition of claim 1 wherein the developing composition comprises anaqueous solution of the developing agent
 9. The composition of claim 1wherein the developing composition also includes a surfactant.
 10. Anetchant or RTV stripper comprising the composition of claim 1.